The present invention pertains generally to a hydraulic mount for vibration damping and, particularly, a vehicle engine hydraulic mount assembly including an air or gas spring supported decoupler which provides gradual transition from low dynamic stiffness to high dynamic stiffness.
Hydraulic vibration damping mounts are well known of the type that generate damping in a predetermined frequency range of vibrations by pumping a hydraulic fluid through an orifice track of predetermined dimensions. The dimensions of the orifice track are typically such that the hydraulic fluid resonates at certain frequencies of input vibration which can result in an increased level of dynamic stiffness of the mount. Hydraulic mounts may also be provided with devices known as decouplers which are disposed in a space formed within the mount orifice plate, for example, and allowed limited free travel within the space to short circuit the fluid from flowing through the orifice track, thus generating a low magnitude of dynamic stiffness necessary to provide isolation of certain vibrations. When the input vibration to the mount exceeds the allowable limit of the free motion of the decoupler, the hydraulic fluid flows through the orifice track thereby generating the mount damping characteristics.
In many hydraulic mount applications, the rate of change of dynamic stiffness of the mount near the tuned frequency should be gradual. However, hydraulic mounts without decouplers do not offer this performance feature, and conventional hydraulic mounts with decouplers must be fabricated with very tight dimensional tolerances of the decoupler and the orifice plate to obtain the desired dynamic stiffness characteristics. For mass produced hydraulic mounts, in particular, the tight dimensional tolerances typically result in a very high scrap rate and difficult manufacturing processes. It is to overcome the problems associated with prior art hydraulic mounts and to provide a mount with the desired dynamic stiffness characteristics near the frequency at which the hydraulic fluid goes into resonance that the present invention has been developed.
The present invention provides an improved hydraulic mount, particularly adapted as a hydraulic engine mount having improved dynamic stiffness characteristics.
In accordance with one aspect of the present invention, a hydraulic mount is provided which includes a decoupler supported or biased by a so-called air or gas spring. In particular, the decoupler is trapped between two orifice plates of an orifice plate assembly for the mount so that one side of the decoupler is in direct communication with a hydraulic pumping chamber of the mount and a layer of air or suitable inert gas is trapped between the other side of the decoupler and a wall surface of the orifice plate. The decoupler is preferably made from a flexible material, such as natural rubber. For low amplitude vibrations input to the mount, the gas spring arrangement provides resistance to motion of the decoupler and consequently the hydraulic fluid is pumped through the orifice track of the mount to generate damping and high dynamic stiffness. Near the frequency at which the hydraulic fluid goes into resonance, the dynamic stiffness of the mount with the gas spring supported decoupler changes gradually as compared with a corresponding mount with no decoupler.
In accordance with another aspect of the invention, a hydraulic mount is provided which includes an arrangement of a decoupler and a gas spring associated with the decoupler which is operable to change the decoupler performance characteristics from that of a conventional decoupled hydraulic mount and to avoid the tight dimensional tolerances required of conventional decoupled hydraulic mounts without sacrificing the mount performance characteristics.
In accordance with still a further aspect of the present invention, a hydraulic mount is provided with a decoupler which is provided with a gas spring or cushion which provides a dynamic rate increase under small displacement vibration inputs to the mount and thus behaves not unlike a non-decoupled mount. However, due to the allowable travel of the decoupler, the response is more linear and the perceived vibrations less harsh in many vehicle applications.
In accordance with yet another aspect of the present invention, a mechanically simple but improved hydraulic mount is provided which includes performance characteristics typically associated with hydraulic mounts with external control features. However, the mount of the present invention is a passive device which allows much larger dimensional tolerances of the mount parts without compromising performance.
Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the present invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawing.